PHYSICS 202 Practice Exam Magnetism, Induction, Simple Harmonic Motion. Name. Constants and Conversion Factors

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Bartholomew Parker
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1 PHYSICS 202 Practice Exam Magnetism, Induction, Simple Harmonic Motion Name Constants and Conversion Factors "* electron charge, / œ Coulombs $" electron mass, 7/ œ kg 1 * # # Coulomb's Constant, 5 œ œ R- 7 / G 41% o -"# # # Permittivity of free space % o œ G ÎR-7 -( Magnetic permeability,. o œ 41 x 10 Tesla-m/Amp Specific heat of Water, -A œ 1.0 cal/g- C 1 calorie œ Joule 1 mole œ #3 atoms 1. A physics student wants to make a home-made transformer which will produce an output voltage of 5 volts when he plugs the transformer into the wall socket (the voltage at the wall socket is 110 volts). To do this he first wraps 250 turns of normal wire around an iron rod. (This is the primary side of the transformer.) This wire can carry a maximum of 1 Ampere. He then wraps a second coil (the secondary coil) around the iron rod made up of larger wire. a. Assuming an ideal transformer, how many turns of this heavier wire will he need to make in order to provide an output voltage in the secondary of 5 volts? b. What maximum current can be drawn from the secondary of this transformer - assuming that the wires in the secondary could handle that much current.

2 Physics 202 Exam III 2 2. A rectangular wire loop is placed flat on frictionless surface. Another long wire is placed beside this loop as shown in the diagram. The long wire carries a constant current of 10 Amperes moving from right to left, as shown in the diagram. At some instant in time, the current in the long wire decreases to 5 Amperes. a. Indicate the direction of the current which is induced in the wire loop. ( Draw this on the loop!) b. What is the direction of the net force which acts on this wire loop while the current in the straight wire is changing? 3. A magnet is moved toward the coil as indicated in the diagram below. Indicate in the rectangular box below the coil the direction of the induced current. N S

3 Physics 202 Exam III 3 4. In the diagram shown below, the outer wire has a total resistance of 2 H and the circular part of the wire has a radius of 10 cm. The battery is a 12 volt battery. R a. When the switch is first closed, the direction of the induced current in the small loop is (circle the correct response): 1) Clockwise 2) Counterclockwise 3) There is no induced current in this wire. b. Determine the magnetic field at the center of the small loop after the current in the outer loop becomes steady. (Assume that the outer loop is approximately a complete circular loop.) c. If the switch in the outer loop is now opened, the direction of the induced current in the small, inner loop is (circle the correct response): 1) Clockwise 2) Counterclockwise 3) There is no induced current in this wire.

4 Physics 202 Exam III 4 5. Two current carrying wires are directed perpendicular to the plane of the page, the upper wire carrying a current into the page, the lower one carrying a current out of the page. Each wire carries a current of 20 Amperes. The distance from each wire to the origin is 2.0 cm. 2 cm y 2 cm x a) Carefully indicate the direction of the magnetic field at the origin due to each wire. b) Determine the magnitude and direction of the net magnetic field at the origin of the coordinate system.

5 Physics 202 Exam III 5 6. Two current carrying wires are placed parallel to each other on the surface of a desk. The distance between the wires is 10 cm. Each wire carries a current of 5 Amperes. The current in wire (1) is going into the paper, while that of wire (2) is coming out of the paper. 10 cm 1 2 a. Indicate on the diagram above the direction of the magnetic field at wire (2) which is caused by the current in wire (1). BE SURE YOU LABEL THIS B! b. Now indicate on the diagram the direction of the force on wire (2) resulting from the magnetic field due to wire (1). BE SURE YOU LABEL THIS F! c. Determine the magnitude of the force per unit length acting on wire (2)? 7. A wire loop with a resistance of 0.5 Ohm/meter is being pulled out of a region of constant magnetic field as shown in the diagram below (i.e., the wire loop is being moved to the right). The velocity of the loop is 20 cm/sec. A constant magnetic field of magnitude of 1.5 Tesla, is directed into the page as shown. 2 cm 5 cm a. Indicate on the drawing the direction of the induced current in the wire.

6 Physics 202 Exam III 6 b. Determine the magnitude of the induced current flowing in the wire. c. Determine the magnitude and direction of the net magnetic force acting on this loop of wire as it is being pulled out of the magnetic field. 8. (15) A spring hangs from the ceiling with a 200 gram mass suspended from it. Its equilibrium position (with this mass attached) is 1 meter below the ceiling. (a) If the mass is pulled downward and released, it oscillates with a period of 0.5 seconds. What will the period of the system be if an additional 300 grams is added to the original mass? (b) What is the spring constant of the spring (in N/m)? (c) With the additional 300 grams attached to the mass spring system, what will the new equilibrium distance below the ceiling be?

7 Physics 202 Exam III 7 9. A 100 gram mass is attached to a spring so that the mass will slide back and forth on the top of a frictionless table. The spring constant is 1000 N/m. (a) What will the period of oscillation of the 100 gram mass be? (b) If the mass is pulled 5cm away from the equilibrium position, how much energy is stored in the spring? (c) What will the maximum velocity of the mass be? 10. The equation of a simple harmonic oscillator is given as: B œ (0.03 m) sin (31t) (a) What is the period of oscillation of this oscillator? (b) What is the frequency? (c) What is the maximum speed of this oscillator? (d) What is the maximum acceleration of this oscillator?

8 Physics 202 Exam III A frog weighing 200 grams hops onto a decorative metal leaf (in the shape of a lilly pad leaf) in the flower garden. This metal leaf (with a mass of 100 grams) is mounted on a spring, so that when the frog first hops on, this leaf-frog-spring system oscillates with a frequency of 3 Hz. While sitting on this decorative leaf the frog satiates himself by catching various critters which are flying around a nearby solar light. As he eats more and more bugs, his mass slowly increases. Each time he flicks out his tongue to catch a bug, the leaf he sits on oscillates up and down for a few seconds (oscillating more slowly each time he catches another meal). After some time, the frog, who is now quite full and heavy, makes one final attempt to catch a last morsel - but because he is so full and tired, he misses. The leaf and frog, however, once more begin to oscillate because of this last ditch effort. The oscillation frequency now is 2.9 Hz. a) Determine the spring constant of the spring. b) Determine the mass of bugs that the frog at that night. [Hint: You can solve this independent of the actual value of the spring constant so that your answer will not depend upon the answer in (a). ]

(D) Blv/R Counterclockwise

(D) Blv/R Counterclockwise 1. There is a counterclockwise current I in a circular loop of wire situated in an external magnetic field directed out of the page as shown above. The effect of the forces that act on this current is